https://github.com/google/guava/guava: Guava is a suite of core and expanded libraries that include utility classes, google's collections, io classes, and much much more. 
/*
 * Copyright (C) 2008 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.primitives;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkElementIndex;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkPositionIndexes;

import com.google.common.annotations.GwtCompatible;
import java.io.Serializable;
import java.util.AbstractList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.RandomAccess;
import org.checkerframework.checker.nullness.qual.Nullable;


Static utility methods pertaining to byte primitives, that are not already found in either Byte or Arrays, and interpret bytes as neither signed nor unsigned. The methods which specifically treat bytes as signed or unsigned are found in SignedBytes and UnsignedBytes. 
See the Guava User Guide article on primitive utilities.

Author:Kevin Bourrillion
Since:1.0
/**
 * Static utility methods pertaining to {@code byte} primitives, that are not already found in
 * either {@link Byte} or {@link Arrays}, <i>and interpret bytes as neither signed nor unsigned</i>.
 * The methods which specifically treat bytes as signed or unsigned are found in {@link SignedBytes}
 * and {@link UnsignedBytes}.
 *
 * <p>See the Guava User Guide article on <a
 * href="https://github.com/google/guava/wiki/PrimitivesExplained">primitive utilities</a>.
 *
 * @author Kevin Bourrillion
 * @since 1.0
 */
// TODO(kevinb): how to prevent warning on UnsignedBytes when building GWT
// javadoc?
@GwtCompatible
public final class Bytes {
  private Bytes() {}

  
Returns a hash code for value; equal to the result of invoking ((Byte)
value).hashCode(). 
Java 8 users: use Byte.hashCode(byte) instead. 
Params:
  • value – a primitive byte value
Returns:a hash code for the value
/**
   * Returns a hash code for {@code value}; equal to the result of invoking {@code ((Byte)
   * value).hashCode()}.
   *
   * <p><b>Java 8 users:</b> use {@link Byte#hashCode(byte)} instead.
   *
   * @param value a primitive {@code byte} value
   * @return a hash code for the value
   */
  public static int hashCode(byte value) {
    return value;
  }

  
Returns true if target is present as an element anywhere in array. 
Params:
  • array – an array of byte values, possibly empty
  • target – a primitive byte value
Returns:true if array[i] == target for some value of i
/**
   * Returns {@code true} if {@code target} is present as an element anywhere in {@code array}.
   *
   * @param array an array of {@code byte} values, possibly empty
   * @param target a primitive {@code byte} value
   * @return {@code true} if {@code array[i] == target} for some value of {@code i}
   */
  public static boolean contains(byte[] array, byte target) {
    for (byte value : array) {
      if (value == target) {
        return true;
      }
    }
    return false;
  }

  
Returns the index of the first appearance of the value target in array. 
Params:
  • array – an array of byte values, possibly empty
  • target – a primitive byte value
Returns:the least index i for which array[i] == target, or -1 if no such index exists.
/**
   * Returns the index of the first appearance of the value {@code target} in {@code array}.
   *
   * @param array an array of {@code byte} values, possibly empty
   * @param target a primitive {@code byte} value
   * @return the least index {@code i} for which {@code array[i] == target}, or {@code -1} if no
   *     such index exists.
   */
  public static int indexOf(byte[] array, byte target) {
    return indexOf(array, target, 0, array.length);
  }

  // TODO(kevinb): consider making this public
  private static int indexOf(byte[] array, byte target, int start, int end) {
    for (int i = start; i < end; i++) {
      if (array[i] == target) {
        return i;
      }
    }
    return -1;
  }

  
Returns the start position of the first occurrence of the specified target within array, or -1 if there is no such occurrence. 
More formally, returns the lowest index i such that Arrays.copyOfRange(array,
i, i + target.length) contains exactly the same elements as target. 
Params:
  • array – the array to search for the sequence target
  • target – the array to search for as a sub-sequence of array
/**
   * Returns the start position of the first occurrence of the specified {@code target} within
   * {@code array}, or {@code -1} if there is no such occurrence.
   *
   * <p>More formally, returns the lowest index {@code i} such that {@code Arrays.copyOfRange(array,
   * i, i + target.length)} contains exactly the same elements as {@code target}.
   *
   * @param array the array to search for the sequence {@code target}
   * @param target the array to search for as a sub-sequence of {@code array}
   */
  public static int indexOf(byte[] array, byte[] target) {
    checkNotNull(array, "array");
    checkNotNull(target, "target");
    if (target.length == 0) {
      return 0;
    }

    outer:
    for (int i = 0; i < array.length - target.length + 1; i++) {
      for (int j = 0; j < target.length; j++) {
        if (array[i + j] != target[j]) {
          continue outer;
        }
      }
      return i;
    }
    return -1;
  }

  
Returns the index of the last appearance of the value target in array. 
Params:
  • array – an array of byte values, possibly empty
  • target – a primitive byte value
Returns:the greatest index i for which array[i] == target, or -1 if no such index exists.
/**
   * Returns the index of the last appearance of the value {@code target} in {@code array}.
   *
   * @param array an array of {@code byte} values, possibly empty
   * @param target a primitive {@code byte} value
   * @return the greatest index {@code i} for which {@code array[i] == target}, or {@code -1} if no
   *     such index exists.
   */
  public static int lastIndexOf(byte[] array, byte target) {
    return lastIndexOf(array, target, 0, array.length);
  }

  // TODO(kevinb): consider making this public
  private static int lastIndexOf(byte[] array, byte target, int start, int end) {
    for (int i = end - 1; i >= start; i--) {
      if (array[i] == target) {
        return i;
      }
    }
    return -1;
  }

  
Returns the values from each provided array combined into a single array. For example, 
concat(new byte[] {a, b}, new byte[] {}, new byte[] {c} returns the array {a, b, c}. 
Params:
  • arrays – zero or more byte arrays
Returns:a single array containing all the values from the source arrays, in order
/**
   * Returns the values from each provided array combined into a single array. For example, {@code
   * concat(new byte[] {a, b}, new byte[] {}, new byte[] {c}} returns the array {@code {a, b, c}}.
   *
   * @param arrays zero or more {@code byte} arrays
   * @return a single array containing all the values from the source arrays, in order
   */
  public static byte[] concat(byte[]... arrays) {
    int length = 0;
    for (byte[] array : arrays) {
      length += array.length;
    }
    byte[] result = new byte[length];
    int pos = 0;
    for (byte[] array : arrays) {
      System.arraycopy(array, 0, result, pos, array.length);
      pos += array.length;
    }
    return result;
  }

  
Returns an array containing the same values as array, but guaranteed to be of a specified minimum length. If array already has a length of at least minLength, it is returned directly. Otherwise, a new array of size minLength + padding is returned, containing the values of array, and zeroes in the remaining places. 
Params:
  • array – the source array
  • minLength – the minimum length the returned array must guarantee
  • padding – an extra amount to "grow" the array by if growth is necessary
Throws:
Returns:an array containing the values of array, with guaranteed minimum length 
    minLength
/**
   * Returns an array containing the same values as {@code array}, but guaranteed to be of a
   * specified minimum length. If {@code array} already has a length of at least {@code minLength},
   * it is returned directly. Otherwise, a new array of size {@code minLength + padding} is
   * returned, containing the values of {@code array}, and zeroes in the remaining places.
   *
   * @param array the source array
   * @param minLength the minimum length the returned array must guarantee
   * @param padding an extra amount to "grow" the array by if growth is necessary
   * @throws IllegalArgumentException if {@code minLength} or {@code padding} is negative
   * @return an array containing the values of {@code array}, with guaranteed minimum length {@code
   *     minLength}
   */
  public static byte[] ensureCapacity(byte[] array, int minLength, int padding) {
    checkArgument(minLength >= 0, "Invalid minLength: %s", minLength);
    checkArgument(padding >= 0, "Invalid padding: %s", padding);
    return (array.length < minLength) ? Arrays.copyOf(array, minLength + padding) : array;
  }

  
Returns an array containing each value of collection, converted to a byte value in the manner of Number.byteValue. 
Elements are copied from the argument collection as if by collection.toArray(). Calling this method is as thread-safe as calling that method. 
Params:
  • collection – a collection of Number instances
Throws:
Returns:an array containing the same values as collection, in the same order, converted to primitives
Since:1.0 (parameter was Collection<Byte> before 12.0)
/**
   * Returns an array containing each value of {@code collection}, converted to a {@code byte} value
   * in the manner of {@link Number#byteValue}.
   *
   * <p>Elements are copied from the argument collection as if by {@code collection.toArray()}.
   * Calling this method is as thread-safe as calling that method.
   *
   * @param collection a collection of {@code Number} instances
   * @return an array containing the same values as {@code collection}, in the same order, converted
   *     to primitives
   * @throws NullPointerException if {@code collection} or any of its elements is null
   * @since 1.0 (parameter was {@code Collection<Byte>} before 12.0)
   */
  public static byte[] toArray(Collection<? extends Number> collection) {
    if (collection instanceof ByteArrayAsList) {
      return ((ByteArrayAsList) collection).toByteArray();
    }

    Object[] boxedArray = collection.toArray();
    int len = boxedArray.length;
    byte[] array = new byte[len];
    for (int i = 0; i < len; i++) {
      // checkNotNull for GWT (do not optimize)
      array[i] = ((Number) checkNotNull(boxedArray[i])).byteValue();
    }
    return array;
  }

  
Returns a fixed-size list backed by the specified array, similar to Arrays.asList(Object[]). The list supports List.set(int, Object), but any attempt to set a value to null will result in a NullPointerException. 
The returned list maintains the values, but not the identities, of Byte objects written to or read from it. For example, whether list.get(0) == list.get(0) is true for the returned list is unspecified. 
Params:
  • backingArray – the array to back the list
Returns:a list view of the array
/**
   * Returns a fixed-size list backed by the specified array, similar to {@link
   * Arrays#asList(Object[])}. The list supports {@link List#set(int, Object)}, but any attempt to
   * set a value to {@code null} will result in a {@link NullPointerException}.
   *
   * <p>The returned list maintains the values, but not the identities, of {@code Byte} objects
   * written to or read from it. For example, whether {@code list.get(0) == list.get(0)} is true for
   * the returned list is unspecified.
   *
   * @param backingArray the array to back the list
   * @return a list view of the array
   */
  public static List<Byte> asList(byte... backingArray) {
    if (backingArray.length == 0) {
      return Collections.emptyList();
    }
    return new ByteArrayAsList(backingArray);
  }

  @GwtCompatible
  private static class ByteArrayAsList extends AbstractList<Byte>
      implements RandomAccess, Serializable {
    final byte[] array;
    final int start;
    final int end;

    ByteArrayAsList(byte[] array) {
      this(array, 0, array.length);
    }

    ByteArrayAsList(byte[] array, int start, int end) {
      this.array = array;
      this.start = start;
      this.end = end;
    }

    @Override
    public int size() {
      return end - start;
    }

    @Override
    public boolean isEmpty() {
      return false;
    }

    @Override
    public Byte get(int index) {
      checkElementIndex(index, size());
      return array[start + index];
    }

    @Override
    public boolean contains(Object target) {
      // Overridden to prevent a ton of boxing
      return (target instanceof Byte) && Bytes.indexOf(array, (Byte) target, start, end) != -1;
    }

    @Override
    public int indexOf(Object target) {
      // Overridden to prevent a ton of boxing
      if (target instanceof Byte) {
        int i = Bytes.indexOf(array, (Byte) target, start, end);
        if (i >= 0) {
          return i - start;
        }
      }
      return -1;
    }

    @Override
    public int lastIndexOf(Object target) {
      // Overridden to prevent a ton of boxing
      if (target instanceof Byte) {
        int i = Bytes.lastIndexOf(array, (Byte) target, start, end);
        if (i >= 0) {
          return i - start;
        }
      }
      return -1;
    }

    @Override
    public Byte set(int index, Byte element) {
      checkElementIndex(index, size());
      byte oldValue = array[start + index];
      // checkNotNull for GWT (do not optimize)
      array[start + index] = checkNotNull(element);
      return oldValue;
    }

    @Override
    public List<Byte> subList(int fromIndex, int toIndex) {
      int size = size();
      checkPositionIndexes(fromIndex, toIndex, size);
      if (fromIndex == toIndex) {
        return Collections.emptyList();
      }
      return new ByteArrayAsList(array, start + fromIndex, start + toIndex);
    }

    @Override
    public boolean equals(@Nullable Object object) {
      if (object == this) {
        return true;
      }
      if (object instanceof ByteArrayAsList) {
        ByteArrayAsList that = (ByteArrayAsList) object;
        int size = size();
        if (that.size() != size) {
          return false;
        }
        for (int i = 0; i < size; i++) {
          if (array[start + i] != that.array[that.start + i]) {
            return false;
          }
        }
        return true;
      }
      return super.equals(object);
    }

    @Override
    public int hashCode() {
      int result = 1;
      for (int i = start; i < end; i++) {
        result = 31 * result + Bytes.hashCode(array[i]);
      }
      return result;
    }

    @Override
    public String toString() {
      StringBuilder builder = new StringBuilder(size() * 5);
      builder.append('[').append(array[start]);
      for (int i = start + 1; i < end; i++) {
        builder.append(", ").append(array[i]);
      }
      return builder.append(']').toString();
    }

    byte[] toByteArray() {
      return Arrays.copyOfRange(array, start, end);
    }

    private static final long serialVersionUID = 0;
  }

  
Reverses the elements of array. This is equivalent to 
Collections.reverse(Bytes.asList(array)), but is likely to be more efficient. 
Since:23.1
/**
   * Reverses the elements of {@code array}. This is equivalent to {@code
   * Collections.reverse(Bytes.asList(array))}, but is likely to be more efficient.
   *
   * @since 23.1
   */
  public static void reverse(byte[] array) {
    checkNotNull(array);
    reverse(array, 0, array.length);
  }

  
Reverses the elements of array between fromIndex inclusive and toIndex exclusive. This is equivalent to 
Collections.reverse(Bytes.asList(array).subList(fromIndex, toIndex)), but is likely to be more efficient. 
Throws:
Since:23.1
/**
   * Reverses the elements of {@code array} between {@code fromIndex} inclusive and {@code toIndex}
   * exclusive. This is equivalent to {@code
   * Collections.reverse(Bytes.asList(array).subList(fromIndex, toIndex))}, but is likely to be more
   * efficient.
   *
   * @throws IndexOutOfBoundsException if {@code fromIndex < 0}, {@code toIndex > array.length}, or
   *     {@code toIndex > fromIndex}
   * @since 23.1
   */
  public static void reverse(byte[] array, int fromIndex, int toIndex) {
    checkNotNull(array);
    checkPositionIndexes(fromIndex, toIndex, array.length);
    for (int i = fromIndex, j = toIndex - 1; i < j; i++, j--) {
      byte tmp = array[i];
      array[i] = array[j];
      array[j] = tmp;
    }
  }
}